The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load.
In a healthy intervertebral disc, the cells within the nucleus pulposus form only about one percent of the disc tissue by volume. These cells produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus with its cushioning qualities. The nucleus pulposus cells may also secrete small amounts of cytokines as well as matrix metalloproteinases (MMPs). These cytokines and MMPs help regulate the metabolism of the nucleus pulposus cells.
In some instances of disc degeneration disease (DDD), gradual degeneration of the intervertebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased loads and pressures on the nucleus pulposus cause the cells within the disc (or invading macrophages) to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors or apoptosis can also cause a decline in the number of disc cells and/or release of toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to provide nutrients to the cells and eliminate waste may result in decreased cell viability and metabolism resulting in further degradation of the ECM along with the accumulation of high levels of toxins that may cause nerve irritation and pain.
As DDD progresses, toxic levels of the cytokines and MMPs present in the nucleus pulposus begin to degrade the ECM. In particular, the MMPs (as mediated by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing its water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the loading pattern within the disc, thereby possibly causing delamination of the annulus fibrosus. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, typically thereby upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain.
U.S. Pat. No. 6,352,557 (“Ferree”) teaches adding therapeutic substances such as nucleus pulposus cells to morselized extra-cellular matrix obtained from donors, and injecting that combination into an intervertebral disc. However, the cells first need to be cultured and then added to the donor matrix prior to implantation into the diseased disc. This process requires a delay in the patient's treatment in addition to subjecting the patient to two separate procedures. The first procedure is to harvest the cells, which then require culturing. Following the culturing the cells are implanted into the patient.
U.S. Pat. No. 6,340,369 (“Ferree II”) teaches harvesting live intervertebral disc cells from a patient, culturing the cells and transplanting them into the affected disc. Ferree II further teaches that the cells can be combined with Type II collagen-glycosaminoglycan matrix or Type I collagen-glycosaminoglycan matrix depending on whether the cells are harvested from the nucleus pulposus (NP) or annulus fibrosus (AF). Also Ferree II suggests adding one or more therapeutic substances to cells prior to transplantation. As an alternate source for cells, Ferree proposes using precursor cells of NP or AF cells, chondrocytes or other living cells that function like or could differentiate into NP or AF cells. Throughout, Ferree teaches that the harvested cells are cultured prior to transplantation.
Alini, Eur. Spine J., 11(Supp.2): S215-220 (2002), suggests that injection of a biomatrix embedded with cells will have the potential to restore functionality to the disc. Alini's experiments are directed to isolating cells from the nucleus pulposus and culturing them. Alini also suggests other sources of cells including disc cells from allogenic donors and autologous stem cells. His teachings suggest that stem cells would be an ideal source but that there are no known methods for culturing the stem cells such that they would differentiate into nucleus pulposus cells prior to implantation. In essence, Alini requires that cells be cultured prior to implantation.
Russell (Abstract 27 ISSLS 2003) reports conducting an experiment to determine whether mesenchymal stem cells (MSCs) could be directed to present disc chondrocyte phenotypes. Russell found that adult human MSCs were induced to differentiate along a chondrocytic phenotype when mediated by culture conditions and also by addition of TGF-B1.
Sakai (Abstract 24 ISSLS 2003) reports evaluating whether autologous transplantation of MSCs to the disc would prevent disc degeneration. Using rabbits, MSCs were isolated from the bone marrow and cultured for 2 weeks prior to transplantation. Results showed significant disc preservation.
Sakai, Biomaterials, 24: 3531-3541 (2003) describes using a final cell density of 1×106 cells/ml, to inject 0.04 ml of solution in which autogenous cultured MSCs were embedded through a 27-gauge insulin injector to each disc. Proliferation of cells after transplantation was found to be successful.
Sobajima (Abstract 43 ISSLS 2002) studied the feasibility of stem cell therapy for DDD. Human NP cells were isolated from patients undergoing disc surgery and were co-cultured with either MSCs from patients undergoing hip surgery or muscle derived stem cells from mice. The data demonstrated a synergistic effect between stem cells and nucleus pulposus cells, resulting in upregulated proteoglycan synthesis in vivo.
Ganey, Eur Spine J, 11 (Suppl.2):S206-S214 (2002), reported on surgeries conducted in Germany where cells were harvested from portions of a patient's disc after discectomy. The cells were then cultured and returned for transplantation into the patient at a later date.
Sander et al. in U.S. Patent Application Publication 2003/0069639, teaches using tissue biopsies taken from a patient as a source to harvest cells for implantation into a degenerated disc.
All of the teachings cited above require culturing of cells prior to implantation, which, in turn, necessitates a delay in treating the patient's degenerating disc.